Method and Device for Producing Flangeless Drawn Parts

ABSTRACT

The invention relates to a method for producing flangeless drawn parts from a flat and/or preformed metal blank using a drawing punch, a blank holder and a drawing die, wherein the drawing die has at least one supporting region and at least one wall region, between which rounded run-in portions are provided, and the blank is trimmed during the drawing operation. In addition, the invention relates to a method for producing flangeless drawn parts from a flat and/or preformed metal blank comprising a drawing punch, a blank holder, a drawing die with at least one supporting region, at least one wall region and rounded run-in portions, which are provided between the supporting region and the wall region.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a continuation of PCT/EP2012/057526, filedApr. 25, 2012, which claims priority to German Application No.102011050001.4, filed Apr. 29, 2011, the entire teachings and disclosureof which are incorporated herein by reference thereto.

FIELD OF THE INVENTION

The invention relates to a method for producing flangeless drawn partsfrom a flat and/or preformed metal blank using a drawing punch, a blankholder and a drawing die, wherein the drawing die has at least onesupporting region and at least one wall region, between which roundedrun-in portions are provided, and the blank is trimmed during thedrawing operation. In addition, the invention relates to a device forproducing flangeless drawn parts from a flat and/or preformed metalblank comprising a drawing punch, a blank holder, a drawing die with atleast one supporting region, at least one wall region and rounded run-inportions, which are provided between the supporting region and the wallregion.

BACKGROUND OF THE INVENTION

It is generally known when producing flangeless drawn parts to producethese firstly by deep drawing a flat blank and separating the resultingflange after the deep drawing process. However, this requires twocost-intensive steps. Moreover, said method does not allowprocess-integrated calibration of the drawn part. Consequently, a thirdstep is required to calibrate the flangeless drawn part. Furthermore, itis known from technical reference book, ‘Schnitt-, Stanz- andZiehwerkzeuge’, Öhler and Kaiser 8^(th) Edition (2001), Springer Verlagpage 428 ff., to produce flangeless drawn parts using a device in whichthe blank is deep drawn and at the same time the supporting region aboveit is trimmed in one stroke of the press. The blank is trimmed in thismethod during the drawing operation in the region of the drawing edge,i. e. in the region of the rounded run-in portions between thesupporting region and the wall region. Since in the region of thedrawing edge, i. e. in the rounded run-in portion between the supportingregion and wall region, the material moves forward in the direction ofthe bottom region of the drawn part, when the plate material is extrudedby the cutting edge of the drawing punch in contact with the roundedrun-in portion, not only an extrusion of the plate material takes place,but also a hardening thereof. This is why an unclean cut is producedduring process-integrated trimming of the blanks during the deep drawingoperation in the region of the rounded run-in portions in this method orusing this device respectively. The reference book cited above pointsout that this method is only used if a clean cut of the edges of thedrawn part is not an issue. In other words, the drawn part must besubjected to further processing.

Proceeding from this prior art, the problem to be solved by the presentinvention is to provide a method and a device for producing flangelessdrawn parts, by means of which flangeless drawn parts can be produced ina process-integrated manner by drawing and trimming in a single strokeof the press while nevertheless being trimmed cleanly.

SUMMARY OF THE INVENTION

According to a first teaching of the present invention, theabove-mentioned problem is solved for a method according to theinvention by the blank being trimmed in the supporting region, while thedrawing operation has not yet been completed, in such a way that thepart of the blank that remains in the supporting region is completelydrawn into the wall region of the drawing die when the drawing punch ismoved further into the drawing die.

The blank is therefore trimmed according to the invention in thesupporting region and not in the region of the rounded run-in portionsor the drawing edge. Thus, the cutting direction and the direction ofmovement of the blank material can be substantially perpendicular toeach other. The blank does not harden immediately through trimming andconsequently a clean trimmed edge is produced. By moving the drawingpress into the drawing die, the part of the blank that remains in thesupporting region is completely drawn into the wall region and aflangeless drawn part with a clean cutting edge is produced in a singlestroke of the press. The method according to the invention ischaracterised in particular by a single step and in this respect isparticularly cost-effective. If preformed blanks are worked, these may,for example, produce excess material, in the bottom region, for example,and consequently calibration of the drawn part is possible in aprocess-integrated manner upon reaching the end position of the drawingpunch. Trimming takes place preferably in the transition region betweensupporting region and drawing radius.

In accordance with a first embodiment of the method according to theinvention, the blank holder is in contact with the region of the blankto be separated while the blank is being trimmed and can thus be used tocontrol the trimming of the blank. The blank holder can ensure, inparticular, that the flow of material is precisely controlled during thetrimming operation in the supporting region. Furthermore, if a wideblank holder and a supporting region are used, a semi-finished part canbe clamped in a crease-free manner and ironed.

The method according to the invention can be carried out in aparticularly easy manner in that the blank is trimmed using a firstcutting edge of the drawing punch and a recess provided in thesupporting region of the drawing die. The cutting edge arranged in thepunch makes it possible to dispense with additional measures, such as anadditional punch and a device to control the movement of the same. Themethod can be implemented more cost-effectively due to thesimplification of the device. The recess in the drawing die serves tohouse the trimmed blank and the cutting punch.

Alternatively, the blank can be trimmed using a cutting edge provided onthe recess of the drawing die, which is arranged preferably in thesupporting region or in the transition region between the supportingregion and the drawing radius.

The method according to the invention can therefore be configured in afurther advantageous manner where the blank is calibrated using anedging section arranged in the drawing die after trimming in the drawingdie through the drawing punch reaching its end position. Deep drawing,trimming and calibration thus take place in the same device in a singlestroke of the press. The drawn parts produced are particularlydimensionally accurate and have less tendency to spring back due tocalibration.

If the blank is profiled after trimming in the supporting region or inthe transition region between the supporting region and the drawingradius using the rounded run-in portions of the drawing die and theedging section of the drawing punch configured as a cutting edge, theblank can also be trimmed in a tension-free manner when drawn into thewall region consequently also achieving particularly good cuttingquality. Moreover, profiling reduces inaccuracies on account ofirregular drawing in of the blank to a minimum and consequentlyextremely dimensionally accurate drawn parts can be produced.

Moreover, the method according to the invention can be further improvedby using a drawing punch, which provides the first and/or second cuttingedge via a replaceable insertion piece in the drawing punch andoptionally using a drawing die, which provides the recess in thesupporting region via a replaceable insertion piece. The first and alsothe second cutting edge as well as the recess in the supporting regionof the blank are exposed to high wear and tear from cutting operations.If these are designed as insertion pieces that are replaceable, accountcan be taken of wear and tear and, where necessary, the respectiveinsertion piece easily replaced.

Alternatively, the first cutting edge is located on the recess in thesupporting region of the drawing die which can also be provided via areplaceable insertion piece. In this case, the drawing punch is alsoequipped with a replaceable insertion piece, which is rounded in theregion of the interaction with the cutting edge on the drawing die. Theinteraction between the cutting edge (sharp edge) and the roundedportion creates a self-centering effect which results in good cuttingquality.

Alternatively, it is also possible in accordance with a furtherembodiment of the method according to the invention, to arrange formaterial, preferably in the form of bars to stand along the cuttingline, region by region, i. e. to produce an uninterrupted cutting line,whereby the drawn part is still at least partially connected to thetrimmed region and at the same time can be removed from the tool (scrapmetal removal via bars). In a further separating process, the trimmedregion can be separated from the good part.

According to a further embodiment of the method according to theinvention, a ‘slotted semi-finished product can be used, which has atleast one slit, preferably at least two slits, which runs from an edgeof the semi-finished product to the cutting line, whereby the trimmedregion breaks into a plurality of individual parts during trimming(division of scrap) and as a result, the bad part is easier to removefrom the tool, via scrap slides, for example.

According to a second teaching of the present invention, theabove-mentioned problem is solved by a generic device in that thedrawing punch has a first cutting edge or rounded portion, which is incontact with a recess provided in the supporting region of the drawingdie with a rounded portion or cutting edge such that the blank in thesupporting region is trimmed during the drawing operation before thedrawing punch reaches its end position. As already stated above, saidcutting edge enables a clean cutting edge to be produced due to theslight hardening in the sheet. As a result, the flangeless drawn part isprovided with a clean cutting edge and is thus significantly moredimensionally accurate in spite of process-integrated trimming.

The interaction between the cutting edge on the first tool part and theopposite rounded portion on the second tool part not only has a positiveinfluence on the cutting result, but also has the advantage, due to theself-centering effect, that the tool parts can be used in conventionaldeep drawing presses, which do not usually have precise and accuratepunch guiding, and thus the design of the tool can be kept simple.

According to a further embodiment of the device, the drawing punch hasan edging section, which after drawing the blank into the wall region,calibrates the blank by compressing at least the wall region of theblank once the drawing punch has reached its end position in the drawingdie. The edging section is configured such that it compresses the wallregion against the bottom region and consequently there is calibrationand thus an improvement in the dimensional accuracy of the drawn part.

According to a further embodiment of the device according to theinvention, the edging section of the drawing punch is configured as asecond cutting edge, wherein the second cutting edge enables profilingof the trimmed blank during the drawing operation in contact with therounded run-in portions. As already indicated above, the second cuttingedge enables additional profiling of the region of the blank drawn intothe wall region. Since in this case the separated trimmings are notexposed to any tensile strain, this profiling is also carried out with aparticularly high degree of precision. Moreover, very few inaccuraciesresult before the end of the drawing process due to profiling because ofthe irregular drawing in of the blank. Consequently, the level ofdimensional accuracy of the respective blanks is particularly high.

In addition, the device according to the invention can be improved byusing a replaceable insertion piece to form the recess of the drawingdie. The recess is, as already mentioned above, exposed to increasedwear and tear due to cutting operations, and thus replacing theinsertion piece only incurs minimal cost.

The same also applies to a further embodiment according to which thefirst cutting edge and/or the edging section of the drawing punch isformed by a replaceable insertion piece. Parts affected by wear and tearcan also be replaced at low cost here.

The object of providing a method and a device for producing flangelessdrawn parts with which flangeless drawn parts can be produced in aprocess-integrated manner by drawing and trimming in a single stroke ofthe press, while nevertheless being trimmed cleanly, is achieved for amethod by the blank being trimmed in the supporting region while thedrawing operation has not yet been completed, in such a way that thepart of the blank that remains in the supporting region is completelydrawn into the wall region of the drawing die when the drawing punch ismoved further into the drawing die.

BRIEF DESCRIPTION OF THE DRAWINGS

Furthermore, the invention shall be explained in detail usingembodiments in conjunction with the drawings.

FIG. 1 shows a sectional view of the process-integrated cuttingoperation during the production of flangeless drawn parts known from theprior art,

FIG. 2 a), b) shows a first embodiment of a device according to theinvention and

FIG. 3 a), b) shows a second embodiment of a device according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Firstly, FIG. 1 shows a schematic sectional view of the method knownfrom the prior art in which a blank 2 is deep drawn using a drawingpunch 1 during the drawing operation and is cut at the same time in thedrawing die 3 using a first cutting edge 4 of the drawing punch 1. Theblank 2 is usually held here by a blank holder 5. Whilst the drawingpunch 1 is moved into the drawing die 3, the material of the blank 2 andthe drawing punch 1 are moved accordingly in the direction of the arrowshown. At the start of the cutting operation of the cutting edge, asshown in FIG. 1, the cutting edge 4 produces hardening due to thevarying rapid movement in the region 2 a of the blank 2. At the sametime, however, the cutting edge 4 separates the blank 2 from the otherpart of the blank in the region of the rounded run-in portion betweenthe supporting region 3 a and the wall region 3 b. Due to the hardeningand the simultaneous tensile strain on the blank 2 in the cuttingregion, an unclean cutting edge is produced, which is avoided with themethod according to the invention.

FIG. 2 a) shows a first embodiment of a device according to theinvention with a drawing punch 1′, which forms a flat blank 2′ in adrawing die 3′ at the start of the drawing process. The cutting edge 4′of the cutting punch 1′ is configured such in the present embodimentthat said cutting edge trims the blank 2′ in the supporting region 2 a′.Trimming can also take place in the transition region between thesupporting region and the drawing radius. It is in contact with a recess7′ of the drawing die 3′ for this purpose. The blank holder 5′ pressesdown the blank 2′ during the first cutting operation using the cuttingedge 4′ in the supporting region 2 a, and consequently a controlledtrimming of the blank 2′ occurs. The remaining part of the blank 2′ iscompletely drawn into the wall region 2 b′ when the drawing punch 1′ ismoved further into the drawing die 3′ and forms the wall region of theblank. As can be seen in FIG. 2 b), the blank 2′ is compressed at theend of the drawing operation using the edging section 6′. However, byselecting the length of the edging section 6′, the drawing operation canalso be completed without calibration or edging of the drawn part.

Moreover, it is also possible to form a pre-formed blank. This canprovide excess material, for example in the bottom region 2 c, whichresults in calibration of the drawn part when the drawing punch 1′reaches its end position.

By trimming the blank in the supporting region 3 a′, the material of theblank 2′ moves perpendicular to the cutting movement of the cutting edge4′ of the drawing punch 1′. As a result of this, minimal hardeningoccurs in the blank 2′ during the cutting operation and a cleaner cut ofthe blank is guaranteed.

As shown in the first embodiment in FIGS. 2 a) and 2 b), the firstcutting edge 4′ and/or the edging section 6′ are realised preferablythrough a replaceable insertion piece in the cutting punch. Thisimproves maintenance and reduces the costs of replacing parts of thedrawing punch affected by wear and tear. The same also applies insofaras the recess 7′ is configured in the drawing die 3′ using a replaceableinsertion piece 8′.

In principle, a blank 2′ can also be heat formed, i. e. the blank isheated to an austenising temperature in advance and heat worked in thedevice according to the invention. This significantly reduces wear andtear in the device, particularly in the case of high-strength steels,since working forces are reduced. Moreover, it is also possible to carryout press hardening after hot forming. The blank 2′ must besystematically cooled at high cooling speed for this purpose in order toenable the formation of a substantially martensitic structure.

FIGS. 3 a) and 3 b) show a further example of a device according to theinvention in a schematic sectional view, which differs from the firstembodiment in that the edging section 6″ is configured as significantlylonger and is provided with a second cutting edge. When the drawingpunch 1″ is moved into the drawing die 3″, the blank 2″ is firstly cutin the supporting region using the cutting edge 4″. The remainingsupporting region, which is drawn into the wall region 2 b″, is alsoprofiled by the edging section 6″ configured as a cutting edge, which,compared with the embodiment in FIG. 2, is configured as longer. Thetrimmings 10″ are produced in the process. As can be seen from FIG. 3b), the trimmings 10″ are under not tensile strain thus enabling cleanseparation of the trimmings 10″. This guarantees extremely good cuttingquality. Moreover, the blank 2″ is only moved slightly into the drawingdie 3″ after profiling thus enabling particularly high dimensionalaccuracy of the flangeless drawn part.

As a result, a flangeless drawn part can be drawn, trimmed, profiled andalso calibrated in a single working stroke using the method according tothe invention. This leads to particularly economical production offlangeless, highly dimensionally stable drawn parts.

In general, influence can also be exerted on the inward movement of theblank to be profiled where trimming is moved locally in the direction ofthe supporting region, i. e. opposite to the drawing radius and/or wherea supporting region varying locally in height is used. Thus, the inwardmovement can be controlled, adjusted, corrected or compensated.

1. Method for producing flangeless drawn parts from a flat and/orpreformed metal blank comprising using a drawing punch, a blank holderand a drawing die, wherein the drawing die has at least one supportingregion and at least one wall region between which rounded run-inportions are provided and the blank is trimmed during the drawingoperation, wherein the blank is trimmed in the supporting region, whilethe drawing operation has not yet been completed, in such a way that thepart of the blank that remains in the supporting region after trimmingis completely drawn into the wall region of the drawing die when thedrawing punch is moved further into the drawing die, wherein the blankis trimmed using a first cutting edge or rounded portion of the drawingpunch and a recess provided in the supporting region of the drawing die.2. Method according to claim 1, wherein the blank holder is in contactwith the region of the blank to be separated during the trimming of theblank.
 3. Method according to claim 1, wherein the blank is trimmedusing a cutting edge provided on a recess of the drawing die.
 4. Methodaccording to claim 1, wherein the blank is calibrated after trimming inthe drawing die when the drawing punch reaches its end position using anedging section arranged in the drawing punch.
 5. Method according toclaim 1, wherein after trimming the blank in the supporting region theblank is profiled by the edging section of the drawing punch configuredas a second cutting edge which is in contact with the rounded run-inportions of the drawing die.
 6. Method according to claim 1, wherein adrawing punch is used, which provides the first and/or second cuttingedge via a replaceable insertion piece in the drawing die and optionallyuses a drawing die, which provides the recess in the supporting regionvia a replaceable insertion piece.
 7. Device for producing flangelessdrawn parts from a flat and/or preformed metal blank for implementing amethod according to claim 1, the device comprising: a drawing punch; ablank holder; a drawing die with at least one supporting region, atleast one wall region and rounded run-in portions which are providedbetween the supporting region and the wall region; and wherein thedrawing punch has a first cutting edge or rounded portion which is incontact with a recess provided in the supporting region of the drawingdie with a rounded portion or cutting edge such that the blank istrimmed in the supporting region during the drawing operation before thedrawing punch reaches its end position, wherein the drawing die and thedrawing punch are configured such that when the drawing die reaches itsend position the blank is completely drawn into the wall region andforms a flangeless drawn part.
 8. Device according to claim 7, whereinthe drawing die has an edging section, which compresses the blank afterthe blank has moved into the wall region by compressing at least thewall region of the blank when the drawing punch reaches its end positionin the drawing die.
 9. Device according to claim 7, wherein an edgingsection of the drawing punch is configured as a second cutting edge andthe second cutting edge enables profiling of the trimmed blank duringthe drawing operation in contact with the rounded run-in portions. 10.Device according to claim 7, wherein replaceable insertion pieces areprovided for provision of the recess in the drawing die.
 11. Deviceaccording to claim 7, wherein replaceable insertion pieces are providedfor provision of the first cutting edge and/or the edging section of thedrawing punch.